title: cAMP signaling regulates platelet myosin light chain (MLC) phosphorylation and shape change through targeting the RhoA-Rho kinase-MLC phosphatase signaling pathway.
abstract: Cyclic adenosine monophosphate (cAMP)-dependent signaling modulates platelet shape change through unknown mechanisms. We examined the effects of cAMP signaling on platelet contractile machinery. Prostaglandin E1 (PGE1)-mediated inhibition of thrombin-stimulated shape change was accompanied by diminished phosphorylation of myosin light chain (MLC). Since thrombin stimulates phospho-MLC through RhoA/Rho-associated, coiled-coil containing protein kinase (ROCK)-dependent inhibition of MLC phosphatase (MLCP), we examined the effects of cAMP on this pathway. Thrombin stimulated the membrane localization of RhoA and the formation of a signaling complex of RhoA/ROCK2/myosin phosphatase-targeting subunit 1 (MYPT1). This resulted in ROCK-mediated phosphorylation of MYPT1 on threonine 853 (thr(853)), the disassociation of the catalytic subunit protein phosphatase 1δ (PP1δ) from MYPT1 and inhibition of basal MLCP activity. Treatment of platelets with PGE1 prevented thrombin-induced phospho-MYPT1-thr(853) in a protein kinase A (PKA)-dependent manner. Examination of the molecular mechanisms revealed that PGE1 induced the phosphorylation of RhoA on serine(188) through a pathway requiring cAMP and PKA. This event inhibited the membrane relocalization of RhoA, prevented the association of RhoA with ROCK2 and MYPT1, attenuated the dissociation of PP1δ from MYPT1, and thereby restored basal MLCP activity leading to a decrease in phospho-MLC. These data reveal a new mechanism by which the cAMP-PKA signaling pathway regulates platelet function.
authors.affiliation: Centre for Cardiovascular and Metabolic Research, Hull York Medical School, University of Hull, Hull, United Kingdom.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Aburima
authors.forename: Katie S
authors.initials: KS
authors.lastname: Wraith
authors.forename: Zaher
authors.initials: Z
authors.lastname: Raslan
authors.forename: Robert
authors.initials: R
authors.lastname: Law
authors.forename: Simbarashe
authors.initials: S
authors.lastname: Magwenzi
authors.forename: Khalid M
authors.initials: KM
authors.lastname: Naseem
mesh_terms: D000527:Alprostadil / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects / Q000201:enzymology* / Q000648:ultrastructure; D048430:Cell Shape / Q000187:drug effects / Q000502:physiology; D000242:Cyclic AMP / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D006801:Humans; D066298:In Vitro Techniques; D046912:Multiprotein Complexes; D009219:Myosin-Light-Chain Kinase / Q000097:blood / Q000378:metabolism*; D043263:Myosin-Light-Chain Phosphatase / Q000502:physiology*; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D010769:Phosphothreonine / Q000378:metabolism; D054645:Protein Phosphatase 1 / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D021122:Protein Subunits; D015290:Second Messenger Systems / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D013917:Thrombin / Q000494:pharmacology; D054460:rho-Associated Kinases / Q000502:physiology*; D020742:rhoA GTP-Binding Protein / Q000502:physiology*
chemical_list: D046912:Multiprotein Complexes; D021122:Protein Subunits; D010769:Phosphothreonine; C066737:RHOA protein, human; D010768:Phosphoserine; D000242:Cyclic AMP; C515852:ROCK2 protein, human; D054460:rho-Associated Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D009219:Myosin-Light-Chain Kinase; D054645:Protein Phosphatase 1; D043263:Myosin-Light-Chain Phosphatase; C490372:PPP1R12A protein, human; D013917:Thrombin; D020742:rhoA GTP-Binding Protein; D000527:Alprostadil